You have had an accident. Now it is necessary for the insurance company to assign who is at fault. Fault is blame: put or pin the blame on. If you hit a telephone pole then you are at fault. This is a collision because you have hit an object with your vehicle. If you have been in an accident with one or more vehicles then the fault has to be decided.
In regards to an automobile collision fault is determined by the company adjuster. It does not matter if the adjuster is employed by your insurance company or is an independent who has been appointed to assist in the examination of the circumstances. Certain situations will be regarded as being at fault - if you rear end the car in front of you is one instance. The premise is that you should always allow a space cushion for proper stopping distance. Often insurance companies have agreements with each other in how they handle a certain claim situation.
The particular circumstances of a collision may lead to a conclusion that more than one driver was negligent. Each driver's insurance company discusses the situation to determine what percentage of responsibility is to be assigned to each person. If you disagree with the decision then your option is to proceed with a court action to resolve it. Sometimes the insurance companies cannot agree and will take the claim to court as well.
A claims situation can involve forensic examination of the evidence. There are specialty companies that look into the circumstances of a claim. It can involve much more than the statements made by the two drivers, witness reports, the police report and the damage to the vehicles.
If you have an SEF 39 endorsement on your schedule of insurance then it is likely your rating will not be affected on your renewal. Once you sue this coverage you will be disqualified until you attain the necessary years of claims-free driving. If you don't see this endorsement on your schedule and you have not had a claim then discuss this with your agent or broker. Perhaps the company you are dealing with now does not offer the "get out of jail free" card. You might want to check and see who does.
Fault